then you can install WiiSystemMenu, and go in settings, there is a menu where you can change the sensitivity of the IR too (remember, all setting used in systemmenu will be reset), but in this menu you can see you IR led in the screen. I remember if I have the max sensitivity, the wiimote see lots of reflection, and sun behind the windows...
So you find the good sensitivity in the Wiimenu, then you fix the setting in Dolphin menu